Hydrogen fuel is one of the most important areas of research in the field of renewable energy development and production. Hydrogen gas can be generated by fuel cells, water electrolyzers, and heterogeneous nanoscale catalysts. It can be burned to directly release chemical energy or condensed for storage and transport, providing fuel for combustion devices or storing excess energy generated by renewable sources such as wind turbines and concentrated solar power assemblies. While platinum is the most active catalyst for hydrogen reduction, its high cost significantly deters its utilization in advanced photocatalytic materials. One approach to mitigating this expense is optimizing the morphology and placement of nanostructured platinum catalysts. Highly crystalline, morphologically-controlled platinum nanoparticles (Pt NPs) have been effectively utilized to increase hydrogen generation efficiency in a variety of nanocomposite materials. However, synthesis routes to high-quality Pt NPs can be dangerous and difficult to replicate. Furthermore, utilization of the Pt NPs in nanocomposite materials is hindered by lack of control over catalyst placement. Nanopeapods are versatile nanocomposites that offer a high degree of control over catalyst placement as well as the potential for interesting new properties arising from the interaction between the catalyst and a semiconductor. Platinum@hexaniobate nanopeapods (Pt@HNB NPPs) consist of linear arrays of Pt NPs encapsulated within the scrolled semiconductor hexaniobate. Pt@HNB NPPs offer significant advantages over similar composites by utilizing the isolated reduction environment of the encapsulated Pt NP arrays to decrease kinetic competition and surface crowding. This work describes the design, fabrication, and implementation of the new nanocomposite platinum@hexaniobate nanopeapods for sensitized hydrogen production under visible light irradiation. The following chapters present facile microwave heating syntheses of highly crystalline Pt nanocubes and Pt@HNB NPPs with consistent morphology and high catalyst loading. A detailed study is also presented of the optical properties of the Pt nanocubes, which produced a UV-range absorbance band that indicates the formation of a localized surface plasmon resonance. Most significantly, preliminary results from visible light photolysis indicate that sensitized Pt@HNB NPPs produce hydrogen in quantities comparable to published systems, and that alteration of experimental parameters may result in even greater yields.

Abstract Water contamination is a global problem and the growing utilization of limited water resources creates a need for efficient purification methods. Industrial effluents are polluting the natural waters, e.g. uncontrolled mining activities in developing countries have created numerous environmental hazards and different types of pollutants. This study focuses on novel adsorbents and photocatalytic materials in order to reach the aim of more efficient and affordable water treatment. This thesis aimed at making active, efficient, and viable adsorbents out of waste materials, as well as using photocatalysis in water treatment for organic pollutants originating from different types of industries. Local Peruvian agro-waste was used as a precursor for activated carbon that was used in adsorption studies for single (As(V) and methylene blue, MB), and multicomponent mixtures (As(V)/Pb/Cd), and real polluted river water. An industrial intermediate product, hydrous TiO2, was used for As(III)/As(V) removal. Photocatalytic materials included a commercial photoactive TiO2 (P25), and tailor-made TiO2 based nanofibers (NF) decorated with Pt/Pd. The results show that the agro-waste based activated carbons show high potential as adsorbents (e.g. ~100% As(V) removal in 2 h). With the multicomponent solution there is evidently competition for the adsorption sites; Pb was removed most efficiently. The specific surface area and pore size distribution play an important role in MB adsorption, as with As(V) the ash content is the most influential parameter. The industrial intermediate product has a high adsorption capacity towards both As(III) and As(V) (over 96% removals in 4 h), and is promising for use in natural and wastewater treatment due to its adsorption properties, availability, low cost, and non-toxicity. Photocatalysis was found to be an efficient removal method for the pollutants tested, also in the diluted industrial wastewater matrix, e.g. diuron was removed 99% in 1 h. The NFs are promising for the efficient photocatalytic degradation of organic effluents in aqueous streams such as wastewaters originating from e.g. biofuel production or fine chemicals and pharmaceutical industry. This study provides new and valuable knowledge for the purification of waters, especially when aiming at developing inexpensive water treatment materials and methods for different applications. / Tiivistelmä Puhtaan veden puute on maailman laajuinen ongelma, ja raskasmetallien ja orgaanisten haitta-aineiden päätymistä ympäristöön ja luonnonvesiin voidaan vähentää hyvällä ja tehokkaalla teollisuuden jätevesien käsittelyllä. Uusia ja tehokkaita, ympäristön kannalta suotuisia ja kestäviä vedenpuhdistustekniikoita tarvitaan erityisesti kehitysmaissa, joissa esim. kontrolloimaton kaivostoiminta aiheuttaa ympäristö- ja terveyshaittoja. Työn kokeellisessa osassa valmistettiin perulaisesta maatalousjätteistä aktiivihiiltä kemiallisella aktivoinnilla, ja seurattiin niiden kykyä adsorboida haitta-aineita (As(V), Pb, Cd, metyleenisini) yksi- ja monikomponenttiliuoksista ja saastuneesta luonnonvedestä (Puyango-Tumbesjoki, Peru). Lisäksi tutkittiin teollisuuden välituotteen (TiO2) aktiivisuutta arseenin, As(III) ja As(V), adsorptiossa. Viimeisessä osiossa tutkittiin valokatalyysiä orgaanisten haitta-aineiden poistossa vesiliuoksista sekä kaupallisella TiO2 P25 -katalyytillä että kokeellisilla Pd/Pt-dopatuilla TiO2 -nanokuiduilla. Tulokset osoittavat, että paikallisesta raaka-aineesta valmistetut aktiivihiilet ovat hyvin potentiaalisia vedenpuhdistusmateriaaleja saavuttaen jopa 100% As(V) poistuman (2h). Adsorboitavien ionien välillä on nähtävissä kilpailua monikomponettiadsorptiossa; lyijyn havaittiin poistuvan tehokkaimmin tutkituissa olosuhteissa. Adsorbentin ominaispinta-ala ja huokoskokojakauma ovat tärkeitä tekijöitä metyleenisinin adsorptiossa, kun taas tuhkapitoisuudella on arseenin adsorptioon suurempi vaikutus. Teollisuuden TiO2-välituotteella havaittiin olevan korkea adsorptiokapasiteetti sekä As(III)- että As(V)-spesieksiä kohtaan saavuttaen yli 96% poistumat (4h). Se on lupaava materiaali edelleen kehitettäväksi ja käytettäväksi esimerkiksi luonnonvesien ja jätevesien puhdistuksessa johtuen sen hyvistä adsorptio-ominaisuuksista, saatavuudesta, edullisuudesta ja myrkyttömyydestä. Valokatalyysin havaittiin olevan toimiva menetelmä orgaanisten molekyylien hajottamiseen, myös laimeasta teollisuuden jätevesimatriisista, esim. diuroni poistui 99% tunnissa. Nanokuitujen tapauksessa aktiivinen metalli vaikutti merkittävämmin reaktion tehokkuuteen kuin ominaispinta-ala. Tämä työ tarjoaa uutta ja tärkeää tietoa vesien puhdistukseen kun tavoitteena on löytää tehokas ja edullinen menetelmä erityyppisiin sovelluksiin.

[ES] La presente tesis doctoral ha centrado la atención en la síntesis de nuevos materiales MOFs obtenidos por intercambio post-sintético de MOFs descritos anteriormente o por heterounión de MOFs estables que tienen estructura UiO66. Estos materiales se han aplicado como fotocatalizadores para la prometedora reacción de división completa del agua que pretende obtener H2 y O2 en forma estequiométrica a partir de agua en ausencia de agentes sacrificantes o nanopartículas metálicas. El nuevo material UiO66 (Zr/Ce/Ti) mostró resultados sorprendentes para la reacción general de división del agua en ambas condiciones de luz UV-Visible e irradiación solar. También se obtuvieron resultados interesantes en el caso del nucleo-corteza UiO66(Zr)-NH225@UiO66(Ce) que, en presencia de agua, cuando se irradió con luz ultravioleta y con luz solar, permitió obtener 550 𝝁 mol*g- 1 de H2 y 350 𝝁 mol*g-1 de H2 en 24 h respectivamente, en las mismas condiciones de trabajo definidas para UiO66(Zr/Ce/Ti). En este trabajo de tesis se presentó por primera vez la posibilidad de reducir 4-NP a través de una metodología tándem que involucra primero la producción de H2 a partir de agua en presencia de metanol, como agente de sacrificio, y UiO66(Zr)-NH2, como fotocatalizador, y la posterior reducción de 4-NP a 4-AP. Por otro lado, se ha demostrado que los materiales defectuosos con estructura de UiO66 pueden reducir selectivamente los dobles enlaces polarizados X=Y en presencia de gas H2. / [CA] La present tesi doctoral ha centrat l'atenció en la síntesi de nous materials MOFs obtinguts per intercanvi post-sintètic de MOFs descrits anteriorment o per heterounió de MOFs estables que tenen estructura UiO66. Estos materials s'han aplicat com fotocatalitzadors per a la prometedora reacció de divisió completa de l'aigua que pretén obtindre H2 i O2 en forma estequiomètrica a partir d'aigua en absència d'agents sacrificants o nanopartícules metàl·liques. El nou material UiO66 (Zr/Ce/Ti) va mostrar resultats sorprenents per a la reacció general de divisió de l'aigua en ambdós condicions de llum UV-Visible i irradiació solar. També es van obtindre resultats interessants en el cas del core-shell UiO66 (Zr) - NH225@UiO66 (Ce) que, en presència d'aigua, quan es va irradiar amb llum ultravioleta i amb llum solar, va permetre obtindre 550 𝝁 mol*g-1 de H2 i 350 𝝁 mol*g-1 de H2 en 24 h respectivament, en les mateixes condicions de treball definides per a UiO66 (Zr/Ce/Ti). En este treball de tesi es va presentar per primera vegada la possibilitat de reduir 4-nitrofenol a través d'una metodologia tàndem que involucra primer la producció de H2 a partir d'aigua en presència de metanol, com a agent de sacrifici, i UiO66 (Zr) -NH2, com fotocatalizador, i la posterior reducció de 4-NP a 4-AP. D'altra banda, s'ha demostrat que els materials defectuosos amb estructura d'UiO66 poden reduir selectivament els dobles enllaços polaritzats X=Y en presència de gas H2. / [EN] The present doctoral thesis has focused the attention on the synthesis of new MOFs materials obtained either by post-synthetic interchange of previously described MOFs or by heterojunction of stable MOFs having UiO66 structure. These materials have been applied as photocatalysts for the promising Overall Water Splitting reaction which claims to obtain H2 and O2 stoichiometrically starting from water in the absence of sacrificial agents or deposited metals nanoparticles. The new material UiO66 (Zr/Ce/Ti) showed surprising results in both UV- Visible light and sunlight irradiation conditions. Interesting results were also obtained in the case of the core-shell named UiO66(Zr)-NH225@UiO66(Ce) which, in the presence of water, when irradiated with both ultraviolet and solar light, allowed to obtain 550 𝝁 mol*g-1 of H2 and 350 𝝁 mol*g-1 of H2 in 24 h respectively, in the same working conditions defined for UiO66 (Zr/Ce/Ti). In this thesis was presented, for the first time, the possibility of reducing 4NP through a tandem methodology which, first, involves the production of H2 from water in the presence of methanol as a sacrificial agent and UiO66(Zr)-NH2 as a photo-catalyst, and subsequent the 4 NP reduction to 4 AP. On the other hand, it has been shown that defective materials with UiO66 structure can selectively reduce polarized X=Y double bonds in the presence of H2 gas. / Melillo, A. (2022). Metal-Organic Hybrid Materials with Catalytic and Photocatalytic Applications [Tesis doctoral]. Universitat Politècnica de València. https://doi.org/10.4995/Thesis/10251/182744 / TESIS

O dióxido de titânio possui diversas aplicações tecnológicas, desde pigmento em tintas, até revestimentos funcionais. É um material resistente à degradação eletroquímica e fotoquímica. Com o aumento da produção industrial de corantes, há um aumento significativo da produção de rejeitos, sendo necessário o desenvolvimento de novas técnicas de degradação, a fim de reduzir a formação de efluentes. Dentre essas técnicas encontram-se os processos oxidativos avançados (POAs), que se baseiam na formação de radicais hidroxila para a degradação dos compostos liberados nos efluentes. A fotocatálise heterogênea utiliza um material semicondutor ativado por radiação ultra-violeta a fim de produzir os radicais hidroxila. Apesar de existirem estudos relacionados à utilização do TiO2 como fotocatalisador, há poucos dados com relação à sua aplicação na forma de filme suportado. Este trabalho teve por objetivos crescer filmes de TiO2 sobre borossilicato, por meio da técnica de deposição química de organometálicos em fase vapor, nas temperaturas de 400 e 500ºC por até 60 minutos, bem como proceder à caracterização microestrutural, morfológica e fotocatalítica desses filmes. Anatase foi a fase identificada em todos os filmes. Os filmes crescidos a 400°C apresentaram estrutura densificada, enquanto que os filmes crescidos a 500°C apresentaram estrutura colunar bem definida. A fotodegradação foi avaliada por meio da degradação do corante alaranjado de metila nos valores de pH 2,00; 7,00 e 10,00. Os resultados de degradação do corante mostraram que a maior eficiência do processo de degradação ocorre em pH = 2. Nessa condição, os melhores resultados ocorrem com o filme crescido por 30 minutos a 400°C, que apresentou 65,3% de degradação. / Titanium dioxide has many technological applications, as pigment in paints, and functional coatings. It is resistant to electrochemical and photochemical degradation. The increase of the industrial production of dyes results in a significant increase in production of wastes, which requires the development of new degradation techniques to reduce the release of effluents. Among these techniques there is the advanced oxidation process (AOP), which is based on the formation of hydroxyl radicals to the degradation of the compounds in the effluent released. The heterogeneous photocatalysis uses a semiconductor material activated by UV radiation to yield hydroxyl radicals. Although there are studies regarding the use of TiO2 as photocatalyst, there are few data related to its application in the form of supported film. The aim of this study was to grow TiO2 films on borosilicate substrate at 400 and 500°C for up to 60 minutes by using metallorganic chemical vapor deposition technique and proceed to the microstructural, morphology and photocatalytic characterization of the films. Anatase phase was identified in all films. The films grown at 400°C presented a densified structure, while the films grown at 500°C showed well defined columnar structure. The photodegradation was assessed by degradation of methyl orange dye in pH 2.00; 7.00 and 10.00. The results of dye degradation showed that the highest efficiency occurred at pH 2. In this condition, the best results occurred for the film grown for 30 minutes at 400°C and presented a degradation of 65.3%.

O presente trabalho teve como objetivos o estudo das propriedades nanoestruturais, características morfológicas e avaliação do comportamento fotocatalítico de filmes de dióxido de titânio dopados com enxofre. Os filmes de TiO2 foram crescidos sobre borossilicato, por meio da técnica de MOCVD, na temperatura de 400 °C. O processo de dopagem com enxofre deu-se a partir do tratamento termoquímico de sulfetação, realizado sob atmosfera de H2 / 2%v. H2S, nas temperaturas de 50 °C, 100 °C e 150 °C, o que resultou em teores de S de 8 at.%, 3 at.% e 0,2 at.%, respectivamente. A degradação do corante alaranjado de metila foi utilizada para avaliar a atividade fotocatalítica dos filmes sob radiação ultravioleta e visível. Todos os filmes exibiram a formação da fase anatase, compostos por grãos bem definidos, e estrutura colunar densificada. Foi observada a formação de grupos SO42- na superfície dos filmes dopados, indicando a substituição dos íons Ti4+ pelo cátion S6+, e a formação da ligação Ti-O-S nos filmes. Os testes de degradação indicaram que os filmes de S-TiO2 apresentam atividade fotocatalítica tanto sob radiação UV, quanto em luz visível. O filme de 8 at.% S-TiO2, dopado a 50 °C, exibiu o melhor comportamento fotocatalítico, com 72,1 % de degradação do corante sob luz visível. Os resultados sugerem que a dopagem com S, além de formar uma morfologia favorável ao processo de fotocatálise, promoveu um deslocamento da absorção do TiO2 para a região do espectro visível, o que consequentemente permite a sua aplicação prática sob luz solar ou lâmpadas de luz visível. / The present work aims the study of the nanostructural properties, morphological characteristics and photocatalytic behavior evaluation of sulfur-doped titanium dioxide films. TiO2 films were grown on borosilicate by MOCVD at 400 °C. Sulfur doping process was carried out by the thermochemical treatment under H2 / 2%v. H2S atmosphere at 50 °C, 100 °C and 150 °C, which resulted in S contents of 8 at%, 3 at% and 0.2 at%, respectively. Methyl orange dye degradation was used to evaluate the photocatalytic activity of the films under UV-Vis radiation. All films exhibited the formation of the anatase phase, composed to well-defined grains, and dense columnar structure. SO42- groups were observed on the surface of all S-doped films, indicating the substitution of the Ti4+ ions by the S6+ cation, and the formation of Ti-O-S bond in the films. Degradation tests indicated that the S:TiO2 films present photocatalytic activity both under UV radiation and visible light. 8 at.% S:TiO2 film, doped at 50 °C, presented a higher photocatalytic performance, with 72.1 % of dye degradation under visible light. The results suggest that the sulfur doping, besides forming a morphology favorable to the photocatalysis process, caused a shift of the TiO2 films absorption to the visible spectrum region, which allows their practical application under sunlight or visible light bulbs.

A presente Tese, elaborada pela integração de artigos científicos publicados ou submetidos em periódicos internacionais, tem por objetivo geral investigar as potencialidades e limitações de resíduos industriais, acadêmicos e agroindustriais na obtenção de catalisadores para degradação de poluentes orgânicos. Foram utilizados resíduos industriais (banhos de galvanização, areias de fundição e petroquímico), acadêmicos (soluções residuais de aula de fotografia contendo prata e solução residual das aulas de química analítica contendo metais) e agro-industriais (casca de arroz, casca de acácia esgotada, pó de fumo) na preparação dos fotocatalisadores suportados. Os sólidos foram caracterizados por um conjunto de técnicas espectroscópicas, volumétricas, microscópicas, eletroquímicas visando descrever os catalisadores do ponto de vista, elementar, estrutural, textural e morfológico, como espectroscopia de emissão de raios X por dispersão de energia (SEM-EDX), espectroscopia de retroespalhamento Rutherford (RBS), espectroscopia de reflectância difusa no ultravioleta (DRS-UV), espectroscopia de espalhamento de raios X em baixo ângulo (SAXS), espectroscopia de fotoelétrons excitados por raios X (XPS), porosimetria de nitrogênio e medidas de potencial zeta (ZP). Os sistemas foram avaliados na fotodegradação de corante (rodamina B), fenol e fármacos sob radiação ultravioleta e visível. Para fins de comparação, titânia comercial P25 (Degussa) foi empregada como catalisador. Além disso, o efeito da reutilização dos catalisadores e atividade fotocatalitica frente a amostras reais foram estudados. O catalisador suportado preparado a partir do resíduo da indústria petroquímica e suportado em sílica apresentou a melhor atividade fotocatalítica na degradação de todas as moléculas testadas, tal como RhB (67 % sob radiação UV e 61 % sob radiação visível), fármaco guaifenesin ( 49 % UV e 45 % visível) e fenol (44 % UV), enquanto que o P25 comercial apresentou 93 % e 14 %, respectivamente, para a radiação ultravioleta e visível. / This thesis, developed by the integration of scientific papers published or submitted in international journals, has the objective to investigate the potential and limitations of industrial waste, academics and agroindustrial to obtain catalysts for degradation of organic pollutants. Industrial waste (galvanic baths, foundry sands and petrochemical), academics (residual solutions of class photograph containing silver and residual solution of analytical chemistry classes containing metals) and agroindustrial (rice husk, exhausted bark acacia, tobacco dust) were used in the preparation of the supported photocatalyst. The solids were characterized by a set of spectroscopic, volumetric, microscopic electrochemical techniques in order to describe elementary structural, textural and morphological properties, such as Scanning electron microscopy with energy dispersive X-ray spectroscopy (SEM-EDX), Rutherford backscattering spectrometry (RBS), diffuse reflectance spectroscopy in the ultraviolet (DRS-UV), small-angle X-ray scattering (SAXS), X-ray Photoelectron Spectroscopy (XPS), nitrogen porosimetry and zeta potential (ZP) measurements. The catalyst activity was evaluated on the dye (RhB), phenol and drugs photodegradation under ultraviolet and visible radiation. For comparative reasons, P25 (Degussa) was also employed as the catalyst. Furthermore, the effect of reuse of catalysts and photocatalytic activity compared to real samples were also evaluated. The silica supported catalyst prepared from petrochemical waste and supported on silica showed the best photocatalytic activity in the degradation of all tested molecules, such as RhB (67% and 61% under UV and visible radiation, respectively), guaifenesin drug (49% UV and 45 % visible radiation) and phenol (44 % UV radiation), while the commercial P25 showed 93 % and 14 %, to ultraviolet and visible radiation, respectively.

O presente trabalho teve como objetivos o estudo das propriedades nanoestruturais, características morfológicas e avaliação do comportamento fotocatalítico de filmes de dióxido de titânio dopados com enxofre. Os filmes de TiO2 foram crescidos sobre borossilicato, por meio da técnica de MOCVD, na temperatura de 400 °C. O processo de dopagem com enxofre deu-se a partir do tratamento termoquímico de sulfetação, realizado sob atmosfera de H2 / 2%v. H2S, nas temperaturas de 50 °C, 100 °C e 150 °C, o que resultou em teores de S de 8 at.%, 3 at.% e 0,2 at.%, respectivamente. A degradação do corante alaranjado de metila foi utilizada para avaliar a atividade fotocatalítica dos filmes sob radiação ultravioleta e visível. Todos os filmes exibiram a formação da fase anatase, compostos por grãos bem definidos, e estrutura colunar densificada. Foi observada a formação de grupos SO42- na superfície dos filmes dopados, indicando a substituição dos íons Ti4+ pelo cátion S6+, e a formação da ligação Ti-O-S nos filmes. Os testes de degradação indicaram que os filmes de S-TiO2 apresentam atividade fotocatalítica tanto sob radiação UV, quanto em luz visível. O filme de 8 at.% S-TiO2, dopado a 50 °C, exibiu o melhor comportamento fotocatalítico, com 72,1 % de degradação do corante sob luz visível. Os resultados sugerem que a dopagem com S, além de formar uma morfologia favorável ao processo de fotocatálise, promoveu um deslocamento da absorção do TiO2 para a região do espectro visível, o que consequentemente permite a sua aplicação prática sob luz solar ou lâmpadas de luz visível. / The present work aims the study of the nanostructural properties, morphological characteristics and photocatalytic behavior evaluation of sulfur-doped titanium dioxide films. TiO2 films were grown on borosilicate by MOCVD at 400 °C. Sulfur doping process was carried out by the thermochemical treatment under H2 / 2%v. H2S atmosphere at 50 °C, 100 °C and 150 °C, which resulted in S contents of 8 at%, 3 at% and 0.2 at%, respectively. Methyl orange dye degradation was used to evaluate the photocatalytic activity of the films under UV-Vis radiation. All films exhibited the formation of the anatase phase, composed to well-defined grains, and dense columnar structure. SO42- groups were observed on the surface of all S-doped films, indicating the substitution of the Ti4+ ions by the S6+ cation, and the formation of Ti-O-S bond in the films. Degradation tests indicated that the S:TiO2 films present photocatalytic activity both under UV radiation and visible light. 8 at.% S:TiO2 film, doped at 50 °C, presented a higher photocatalytic performance, with 72.1 % of dye degradation under visible light. The results suggest that the sulfur doping, besides forming a morphology favorable to the photocatalysis process, caused a shift of the TiO2 films absorption to the visible spectrum region, which allows their practical application under sunlight or visible light bulbs.

This work investigates the elimination of new and emerging microcontaminants (EMs) from water by means of photochemical oxidation processes, namely heterogeneous and homogeneous photocatalysis. Representative compounds of artificial sweeteners (saccharin, SAC), endocrine disruptors (bisphenol-A, BPA), and pharmaceutica ls (antipyrine, AP) of high environmental persistence and widespread occurrence in the water cycle are used as case studies. Novel concepts that can make photochemica l oxidation a more cost-effective and environmentally benign technology are tested. In Chapter 4, the photocatalytic treatment of SAC and BPA is investigated. Novel submicronic anatase-rutile nanocomposite particles with tuned phase ratio are used as catalysts to increase the photocatalytic performance under UVA irradiation. At the best-assayed conditions (C0 = 3 mg/L, catalyst = 400 mg/L), SAC and BPA are completely degraded within 90 and 150 min of photocatalytic treatment, respectively. [variables: anatase-rutile ratio; initial substrate concentration; catalyst concentration; catalyst reuse; sonication during catalyst recovery] In Chapter 5, a UVA light-emitting diode (UVA-LED) and sunlight are used as irradiation sources to reduce energy requirements and environmental impacts of photocatalytic processes. The photocatalytic degradation of SAC and BPA is studied under UVA irradiation provided by either a UVA-LED or a conventional fluoresce nt blacklight UVA lamp (UVA-BL) and solar irradiation. At the best-assayed conditions (C0 = 2.5 mg/L, TiO2 = 250 mg/L), BPA is completely degraded within 20, 30, and 120 min under UVA-LED, solar, and UVA-BL irradiation, respectively. The treatment time required for the complete elimination of SAC is 20 min under UVA-LED and 90 min under UVA-BL irradiation. [variables: initial substrate concentration; catalyst concentration; water matrix; light source; reactor configuration] In Chapter 6, a comparative study is carried out among the photocatalytic systems of Chapters 4 and 5 in terms of EMs removal, photonic and energy efficiencies. Technica l and economic aspects of all the processes are assessed. LED-driven photocatalysis achieves the highest efficiency in terms of organic removal with the minimum energy consumption, rendering it the most sustainable technology for the treatment of EMs. In Chapter 7, olive mill wastewater (OMW) is used as an iron-chelating agent in the photo-Fenton reaction to obviate the need for water acidification at pH 2.8. Conventional, OMW- and EDDS-assisted photo-Fenton treatment is applied for SAC degradation in a solar compound parabolic collector (CPC). It was found that OMW forms iron complexes able to catalyse H2O2 decomposition and generate hydroxyl radicals. At the optimal OMW dilution (1:800), 90% of SAC is degraded within 75 min. [variables: pH; iron-chelating agent; initial SAC concentration; OMW dilution] In Chapter 8, other complexing and oxidising agents, namely oxalate and persulfate, are used for the intensification of AP degradation during UVA-LED photo-Fenton treatment. Neural networks are applied for process modelling and optimisation. At the optimal conditions (hydrogen peroxide = 100 mg/L, ferrous iron = 20 mg/L, oxalic acid = 100 mg/L), complete degradation of AP and 93% mineralisation is achieved within 2.5 and 60 min, respectively. [variables: initial concentration of hydrogen peroxide, ferrous iron, oxalic acid, persulfate] It is concluded that LED-driven photocatalysis is a sustainable technology for the elimination of EMs from water. Results from this work highlight the need for development and optimisation of engineering proper LED reactors. Furthermore, this work introduces a new concept towards the sustainable operation of photo-Fenton that is based on the use of wastewaters rich in polyphenols instead of pricey and hazardous chemicals for iron chelation. The addition of ferrioxalate complexes is proposed for the intensification of EMs mineralisation during UVA-LED photo-Fenton treatment. Finally, the findings of this work encourage the use of chemometric tools as predictive and optimisation tools.

Environmental pollution on a global scale is expected to be the greatest problem that chemical scientists will face in the 21st century, and an increasing number of these scientists are looking to new photocatalytic systems for the solution. Existing photocatalytic systems are effective for the decomposition of many unwanted organics through the use of efficient semiconductor photocatalysts activated by ultra-violet (UV) irradiation. The demand for visible light activated photocatalytic systems is increasing rapidly. Currently, however, the efficiency and availability of photocatalysts which can be activated effectively by the solar spectrum and especially indoor lighting is severely limited. The purpose of this project is to investigate the potential of a TiO2-ZnFe2O4 alloyed nanocomposite for use as a visible light activated photocatalyst. An overview of the principles of photocatalysis is first provided. Relevant properties of pure and modified TiO2 are next discussed, and results of studies on structural and photocatalytic properties are presented. Alloyed TiO2-ZnFe2O4 nanocomposites are discussed in detail and their crystal structure, particle size, particle interaction, optical characteristics, and photoactivity are discussed in detail. Measurements characterizing the alloys are carried out using XRD, SEM, EDS, UV-Vis spectroscopy, and photodegradation procedures. The photoactivity of the alloys is carefully studied through phenol degradation experiments, and recommendations are provided to improve the photocatalysts under investigation.

In this work, a series of simple, rapid and effective photoelectrochemical methodologies have been developed and successfully applied to the study of kinetic and thermodynamic characteristics of photocatalytic oxidation processes at TiO2 nanoparticulate films. As an application of the systematic studies of photocatalytic processes by photoelectrochemical techniques, a rapid, direct, absolute, environmental-friendly and accurate COD analysis method was successfully developed. In this work, the TiO2 nanoparticles colloid was prepared by the sol-gel method. The TiO2 nanoparticles were immobilized onto ITO conducting glass slides by dip-coating method. Thermal treatment was carried out to obtain nanoporous TiO2 films of different structures. At low calcination temperature (below 600°C), nanoporous TiO2 films of pure anatase phase were prepared. At high calcination temperature (above 600°C), nanoporous TiO2 films of mixed anatase and rutile phases were obtained. At these film electrodes, the work was carried out. By employing steady state photocurrent method and choosing phthalic acid as the model compound, the photocatalytic activity of the TiO2 nanoporous films calcined at various temperatures and for different lengths of time was evaluated. It was found that the films with mixed anatase and rutile phases calcined at high temperature exhibited high photocatalytic activity. Based on semiconductor band theory, a model was proposed, which explained well this finding. By employing linear sweep voltammetry (under illumination) and choosing glucose (an effective photohole scavenger) as a model compound, the characteristics of the photocatalytic processes at nanoparticulate semiconductor electrodes were investigated. Characteristics of the nanoporous semiconductor electrodes markedly different from bulk semiconductor electrodes were observed. That is, within a large range of electrode potentials above the flat band potential the electrodes behaved as a pure resistance instead of exhibiting variable resistance expected for bulk semiconductor electrodes. The magnitude of the resistance was dependent on the properties of the electrodes and the maximum photocatalytic oxidation rate at TiO2 surface determined by the light intensity and substrate concentration. A model was proposed, which explained well the special characteristics of particulate semiconductor electrodes (nanoporous semiconductor electrodes). This is the first clear description of the overall photocatalytic process at nanoparticulate semiconductor electrodes. The investigation set a theoretical foundation for employing photoelectrochemical techniques to study photocatalytic processes. By using the transient technique (illumination step method analogous to potential step method in conventional electrochemistry), the adsorption of a number of strong adsorbates on both low temperature and high temperature calcined TiO2 nanoporous films was investigated. Similar adsorption characteristics for different adsorbates on different films were observed. In all the cases, three different surface bound complexes were identified, which was attributed to the heterogeneity of TiO2 surface. The photocatalytic degradation kinetics of the pre-adsorbed organic compounds of different chemical nature was also studied by processing the photocurrent-time profiles. Two different photocatalytic processes, exhibiting different rate characteristics, were observed. This was, again, attributed to the heterogeneity of the TiO2 surface corresponding to heterogeneous adsorption characteristics. The catalytic first order rate constants of both fast and slow processes were obtained for different organic compounds. It was found that for different adsorbates of different chemical nature the magnitudes of rate constant for the slow kinetic process were very similar, while the magnitudes of rate constant for the fast process were significantly affected by the photohole demand characteristics of different adsorbates. Photohole demand distribution that depends on the size and structure of the adsorbed molecules was believed to be responsible for the difference. By employing steady state photocurrent method, the photocatalytic degradation kinetic characteristics of both strong adsorbates and weak adsorbates of different chemical structures were compared at pure anatase TiO2 nanoporous TiO2 films as well as at anatase/rutile mixed phase TiO2 nanoporous film electrodes. At the former electrodes for all the different organic compounds studied, the photocatalytic reaction rate increased linearly with concentration at low concentrations. Under such conditions, it was demonstrated that the overall photocatalytic process was controlled by diffusion and was independent of the chemical nature of organic compounds. However, the linear concentration range and the maximum photocatalytic reaction rate at high concentrations were significantly dependent on the chemical nature of the substrates. This was explained by the difference in the interaction of different organic compounds with TiO2 surface, the difference in their photohole demand distributions at the TiO2 surface and the difference in their nature of intermediates formed during their photocatalytic mineralization. In contrast, at the latter electrodes for the photocatalytic oxidation of different organic compounds the linear ranges (diffusion control concentration range) and the maximum reaction rates at high concentration were much larger than at the former electrodes and much less dependent on the chemical nature of the organic compounds. The spatial separation of photoelectrons and photoholes (due to the coexistence of rutile phase and anatase phase) and the increase in the lifetime of photoelectrons and photoholes are responsible for the excellent photocatalytic activity of the electrodes. By employing the thin-layer photoelectrochemical technique (analogous to the thin-layer exhaustive electrolytic technique), the photocatalytic oxidation of different organic compounds at the mixed phase TiO2 nanoporous electrodes were investigated in a thin layer photoelectrochemical cell. It was found that the charge derived from exhaustive oxidation agreed well with theoretical charge expected for the mineralisation of a specific organic compound. This finding was true for all the compounds investigated and was also true for mixtures of different organic compounds. The photocatalytic degradation kinetics of different organic compounds of different chemical identities in the thin layer cell was also investigated by the photoelectrochemical method. Two kinetic processes of different decay time constants were identified, which were attributed to the degradation of preadsorbed compounds and the degradation of compounds in solution. For the degradation of compounds in solution, a change in the overall control step from substrate diffusion to heterogeneous surface reaction was observed. For different organic compounds, the variation of the rate constant was determined by the photohole demand rather than by the chemical identities of substrates. The kinetics of the fast kinetic process, on the other hand, was greatly affected by the adsorption properties of the substrates. For the strong adsorbates, the rate was much larger than for weak adsorbates. However, the rate constant of the process was independent of the chemical identities of the substrates and the variation of the constant was also determined by the photohole demand. Based on the principles of exhaustive photoelectrocatalytic degradation of organic matter in a thin layer cell, a novel, rapid, direct, environmental-friendly and absolute COD analysis method was developed. The method was tested on synthetic samples as well as real wastewater samples from a variety of industries. For synthetic samples with given compositions the COD values measured by my method agree very well with theoretical COD value. For real samples and synthetic samples the COD values measured by my method correlated very well with those measured by standard dichromate COD analysis method.